Bitmap/PPM conversion through a pipe

From Rosetta Code

Bitmap/PPM conversion through a pipe is a programming task. Visitors like you are encouraged to solve it according to the task description, using any language they may happen to know.

Using the data storage type defined on this page for raster images, delegate writing a JPEG file through a pipe using the output_ppm function defined on this other page.

There are various utilities that can be used for this task, for example: cjpeg (package "jpeg-progs" on Linux), ppmtojpeg (package "netpbm" on Linux), convert (from ImageMagick, multi-platform).

[edit] C

Works with: POSIX version .1-2001 This one uses the ImageMagick convert tool.

/* interface */
void print_jpg(image img, int qual);

#define MAXCMDBUF 100
void print_jpg(image img, int qual)
{
   char buf[MAXCMDBUF];
   unsigned int n;
   FILE *pipe;
 
   snprintf(buf, MAXCMDBUF, "convert ppm:- -quality %d jpg:-", qual);
   pipe = popen(buf, "w");
   if ( pipe != NULL )
   {
           fprintf(pipe, "P6\n%d %d\n255\n", img->width, img->height);
           n = img->width * img->height;
           fwrite(img->buf, sizeof(pixel), n, pipe);
           pclose(pipe);
   }
}

The code that writes to the pipe is the same of output_ppm of course. A complete example is

#include "imglib.h"
 
int main()
{
      image img;
 
      img = alloc_img(100,100);
      fill_img(img, 50, 20, 200);
      draw_line(img, 0, 0, 80, 80, 255, 0, 0);
      print_jpg(img, 75);
      free_img(img);
}

In order to make it working, you must link it with the raster image functions given by the codes here and here

[edit] OCaml

let print_jpeg ~img ?(quality=96) () =
  let cmd = Printf.sprintf "cjpeg -quality %d" quality in
  (*
  let cmd = Printf.sprintf "ppmtojpeg -quality %d" quality in
  let cmd = Printf.sprintf "convert ppm:- -quality %d jpg:-" quality in
  *)
  let ic, oc = Unix.open_process cmd in
  output_ppm ~img ~oc;
  try
    while true do
      let c = input_char ic in
      print_char c
    done
  with End_of_file -> ()
;;

[edit] Ruby

Extends Write ppm file#Ruby. Uses the ImageMagick convert tool. Additionally, for debugging, allow writing in pixmap P3 (ascii) format.

class Pixmap
  PIXMAP_FORMATS = ["P3", "P6"]   # implemented output formats
  PIXMAP_BINARY_FORMATS = ["P6"]  # implemented output formats which are binary
 
  def write_ppm(ios, format="P6")
    if not PIXMAP_FORMATS.include?(format)
      raise NotImplementedError, "pixmap format #{format} has not been implemented" 
    end
    ios.puts format, "#{@width} #{@height}", "255"
    ios.binmode if PIXMAP_BINARY_FORMATS.include?(format)
    @height.times do |y|
      @width.times do |x|
        case format
        when "P3" then ios.print @data[x][y].values.join(" "),"\n"
        when "P6" then ios.print @data[x][y].values.pack('C3')
        end
      end
    end
  end
 
  def save(filename, opts={:format=>"P6"})
    File.open(filename, 'w') do |f|
      write_ppm(f, opts[:format])
    end
  end
 
  def print(opts={:format=>"P6"})
    write_ppm($stdout, opts[:format])
  end
 
  def save_as_jpeg(filename, quality=75)
    pipe = IO.popen("convert ppm:- -quality #{quality} jpg:#{filename}", 'w')
    write_ppm(pipe)
    pipe.close
  end
end
 
image = Pixmap.open('file.ppm')
image.save_as_jpeg('file.jpg')

[edit] Tcl

Referring to Write ppm file#Tcl and Basic bitmap storage#Tcl

Library: Tk

package require Tk
 
proc output_jpeg {image filename {quality 75}} {
    set f [open |[list convert ppm:- -quality $quality jpg:- > $filename] w]
    fconfigure $f -translation binary
    puts -nonewline $f [$image data -format ppm]
    close $f
}

However, it is more normal to do this directly with the Library: TkImg which is bundled with many Tcl distributions.

package require Tk
package require img::jpeg
 
proc output_jpeg {image filename} {
    $image write $filename -format jpeg
}
set img [image create photo -filename filename.ppm]
output_jpeg $img filename.jpg